A century ago, by the unscientific estimate of crab fishermen along the central coast of California, more than 100,000 sea otters (Enhydra lutris nereis) populated the waters between Monterey Bay and Santa Barbara, a distance of about 250 miles. In 2010, the count was less than 2,750.

Numerous factors account for the precipitous decline in population. One is the outright war that the fishing industry declared on the sea otters, creatures brazen enough to steal out of netted catches. Another is the effect of industry proper: factories and agricultural runoff filled the bays and inlets of California with an array of toxins, to disastrous effect for not just sea otters but also marine life of every kind.

Some scientists are now wondering whether an apparent upswing in the number of sharks in the coastal waters along that stretch of California may be having an effect as well, since the only regular predator on the otter is the shark. And why should the sharks be on the move? Apparently, they’re following the growing seal and sea lion populations in the region—a phenomenon we have reported on earlier. Sharks do not particularly care for otters, but it takes a bite for them to determine that it’s not a seal or sea lion that they’ve caught; the sharks spit them out and move on, but the bite is almost always fatal for the otters.

Other scientists hazard that global climate change may also have a role. With that change, storms along the coast have tended to be more intense than in recorded history past; witness the deluges that devastated southern California in the early winter of 2010–11. That stormy weather is particularly perilous for sea otter pups, whose numbers are markedly down; according to the U.S. Geological Survey, the mortality rate is up by some 11 percent between 2010 and the relatively calm year of 2009.

The degradation of kelp forests along the California coast, too, seems to have a part. These marine forests are an extraordinarily productive source of food for many species, not least ones on which the sea otter depends, and these have been in marked decline with both the growth of toxins and the change in climatic conditions. The decline of the kelp forests means a loss of prime otter habitat, since otters sleep atop kelp fronds and use them as shelter in stormy weather. The otters repay the hospitality by eating vast quantities of sea urchins, which, unchecked, would devour the kelp forests in no time. So important are the otters in the life of the kelp forest that they are considered keystone species—that is, species on which many others, and even whole ecosystems, depend.

There are other contributing factors. One, speaking to the power of unintended consequences, is the presence of toxoplasmosis in at least some adult otters in the California population—the result, it appears, of domestic cat feces that have been flushed through mainland sewage systems down into the sea.

Whatever the case and whatever the cause or causes, if the California sea otter has had its ups and downs in recent years, the last few have been particularly marked down ones—defying a trend whereby, in the period from 2000 to 2005, the sea otter seemed to be making a strong comeback. From 2006 to 2007 alone, the population increased by some 12 percent, which gave conservation biologists hope that the sea otter, listed as threatened in the federal roster of endangered species, might one day soon enjoy a full recovery.

Instead, as Otter Project executive director Alison Ford told the Santa Cruz Sentinel, “Otters are the endangered species success story that’s not quite successful. Its population is hovering in decline.”

So far, efforts to stem this decline have been haphazard if well intended. Legislation introduced in Congress in 2004 to protect the southern population of sea otters—a northern one, also in decline, lives along Alaska’s Aleutian Islands—died in committee, and the present Congress seems notably disinclined to address environmental problems, particularly if it involves spending money.

California’s state sea otter fund, to which taxpayers make voluntary contributions, is rapidly shrinking, and, in a time of fiscal crisis, is likely to be terminated. As the Defenders of Wildlife, which is working to keep the program alive, notes, the fund must reach $260,890 in 2011 if this termination is to be staved off. That is a small sum, but given the present antitax sentiment, it may simply be unattainable.

Researchers at the University of California at Santa Barbara observe that even as the number of sea otters falls, their range expands. We might harbor hope, then, that the remaining population will move to more congenial waters, away from humans, cats, and other threats. It is more likely, though, that, as a study of population dynamics concludes, the California sea otter will instead soon move from threatened to fully endangered status.

“Sea otter health can tell us a lot about the health of the coastal waters that humans also enjoy,” Tinker says. “So, we’re eager to learn more.” The condition of the ocean, though, gives him pause. Of the sea otters, he adds, “What they’re telling us is that it’s not doing so well.”

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